Data point to earthquakes causing mysterious Wis. booms

By Jessie Van Berkel, The (Appleton, Wis.) Post-Crescent

CLINTONVILLE, Wis. - Delayed data from seismic monitors has answered lingering questions about booms that have rocked this town since Sunday.

By Ron Page, AP

A resident asks questions at a public meeting with city officials in Clintonville, Wis., on Wednesday. Families long for quiet after mysterious booms over the past few nights roused them from their beds.

A resident asks questions at a public meeting with city officials in Clintonville, Wis., on Wednesday. Families long for quiet after mysterious booms over the past few nights roused them from their beds.

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"The mystery is solved. We have experienced an earthquake here in Clintonville," City Administrator Lisa Kuss said Thursday evening to an auditorium filled with about 250 people.

Several residents questioned the solution. Earlier this week they were told that earthquakes had been ruled out as a potential cause of the sounds that shook them awake for several nights.

"Are you confident that we're safe?" resident Todd Mattes asked.

"I do believe you're safe," Kuss replied.

Other residents of this town of 4,500 about 40 miles west of Green Bay, Wis., asked why they heard such loud booming -- a sound not characteristic of quakes.

The soil and granite under the city is different than that of most earthquake-prone towns and may account for the sharp noises, Kuss said.

Thursday afternoon, geophysicists said it was likely a "swarm of microquakes" responsible for the events this week.

Around 12:15 a.m. Tuesday, a magnitude 1.5 earthquake was detected by traveling portable arrays that record seismic activity, the U.S. Geological Survey announced Thursday.

Researchers don't have many of the devices in Wisconsin and "it was by fluke" that the portable detectors, which move around the country, were positioned near here recently, Kuss said. The readings from those machines, as well as USGS monitors in Linden, Iowa and Lac Vieux Desert, Wis., confirmed Tuesday's quake.

A "microquake" -- quakes of less than 2.0 on the Richter scale are given that designation -- of that size is likely only felt by people within a five-mile radius of the epicenter of the quake, USGS geophysicist Rafael Abreu said.

Events with magnitudes of about 4.5 or greater -- several thousand such shocks occur annually -- are strong enough to be recorded by sensitive seismographs all over the world, the USGS says on its website.

For people near the epicenter, the shaking and noise would resemble a loud truck rumbling past their home, Abreu said.

For an earthquake to damage property, it would have to be above 5.5 magnitude, Kuss said at the public meeting Thursday.

Before the announcement of the microquakes, the city had hired Ruekert & Mielke Inc., an engineering firm from Waukesha, Wis., and shipped in monitors in hopes of getting more data on the sounds. City officials will talk with the engineers and determine whether the analysis is necessary now -- and if anything else can be gleaned about the cause, Kuss said.

The equipment and services were going to cost the city about $7,000 and even if they decide not to go forward with the research, they will have to pay some costs, Kuss said.

For now, it seems that the booms have ceased. Police only received four reports of possible booms Tuesday night into Wednesday morning as opposed to 40, 100 and 150 calls in the nights before, Kuss said, noting that microquakes commonly only last a few days.

Officials can't definitely say that the series of microquakes is the culprit, Abreu said, but such an occurrence is not unheard of and has happened in other parts of the country.

Not everyone is ready to buy into a microquake as the cause. Many residents claimed Thursday that the noises have been going on for months.

The earthquake announcement from USGS "is kind of going to throw everything into a tizzy," said Clifford Thurber, a geophysics professor at the University of Wisconsin-Madison. Before the shaking is attributed to earthquakes, he thinks that the evidence and research needs to be more conclusive.

"If it turns out it's coming from a mile or two deep, yeah, it's small earthquakes," Thurber said. But if the cause is determined to be only about 100 feet deep, then something else is happening, he said.

If the booms stop and Ruekert & Mielke Inc. can't record anything, more sophisticated analysis can be done on the USGS recordings of seismic disturbance, but a definitive answer might not exist, Thurber said.

Booming noises attributed to earthquakes tend to occur more in the Northeast and along the East Coast, according to the USGS. Earthquakes are rare in Wisconsin, and most often have been felt in the southern part of the state.

For Clintonville, this could be a once-in-a-lifetime rumble.

"There's nothing that says because you had one that you're likely to have another," Kuss said.

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